The invention concerns a thermal safety device for automatically blocking pipes, especially gas pipes, if an inadmissible rise in temperature should occur, in accordance with the characterizing clause of the first patent claim.
Such thermal safety devices, installed in pipes, for example in front of gas fittings, gas appliances, gas meters, etc., are available in a variety of designs. Their function is to interrupt the gas supply when there is a rise in temperature before the temperature on the appliances mentioned increases to such an extent that their external sealing is endangered.
In DE-OS 44 22 241, for instance, a thermal valve safety device is described of the type mentioned at the beginning. With this solution there is a closing element in the axial continuation of a seat located within the casing. This closing element is kept in the open position by at least one molding bent approximately into a U-shape. Following a sealing area facing towards the seat, on the side facing away from the seat the closing element forms a throat, to which a preferably cylindrical collar is attached. Both the legs of the molding are therefore located within the area of the throat and thus form a rest for the collar against the force of the closing spring. Furthermore, the part of the molding which links both the legs is propped on a thermal solder element, which is itself adjacent to the internal wall of the casing. Once the thermal solder element has melted away, the legs of the molding, because the molding has consequently changed its position in the casing, are no longer within the throat of the closing element. Under the influence of the closing spring the closing element thus moves to the closed position. Thereby each of the legs forms a guideway directed towards the seat for the collar and/or the sealing area of the closing element.
This solution has the drawback that the casing next to the closing element has many fittings, particularly in the circulation cross section of the closing element. In order to achieve standard specifications or the flow values desired in practice, for example, one is forced to determine the dimensions accordingly, and, as a result, similarly required and/or desired minimal dimensions, especially for installation, cannot be fulfilled.
Furthermore, in EP-PS 605 551 there is a so-called fire-protection valve with a closing spring for automatically shutting off pipes.
With this fire-protection valve a metallic closing element is aligned in a casing. In the sealing area the closing element has a spherical form, with which, under the force of a closing spring, it rests in the open position on three fixed points formed by two balls and a temperature-sensitive component. Both balls, which are themselves propped on a rest in the casing, are at such a distance from each other that they form an acceptance angle of approx. 90.degree.. Opposite this acceptance angle the temperature-sensitive component is secured to the internal wall of the casing.
The component consists of an inwardly-open cup, the base of which is secured to the internal wall. The radially inwardly-open cup contains a solder element, into which a ball forming a clearance fit with the opening of the cup is pressed. The ball forms the third fixed point and is sized so that it is located almost entirely within the cup once the solder has melted. The three fixed points form the diameter of the rest for the metallic closing element, and its dimensions are such that, when the ball is in the cup, the closing element is pushed by the force of the closing spring through the enlarged opening resulting between the three fixed points.
FIG. 1 accompanying this device demonstrates clearly that the drawback of this solution is that the eccentrically positioned closing element is not guided axially when the closing stroke is carried out. The force direction of the closing spring is never perfectly axial because of the existing tolerances, and so in the closing stroke the ball is deflected sideways. The inevitably resulting sideways impact, and the centering movement into the seat which is therefore necessary, consume part of the kinetic energy required to achieve a force fit. Yet this force fit is needed if the thermal valve safety device is still to be effective at temperatures where the closing spring becomes powerless.
A similar solution is described in EP-OS 574 677. With this safety gas outlet, a retaining ring is positioned within the casing, either in or on a rotationally symmetric closing component, the largest external diameter of which is only slightly larger than the internal diameter of the retaining ring. Here the closing component is pressed by a spring component against the retaining ring in the direction of a sealing seat. The retaining ring consists of a material that softens at is a pre-selected, determined temperature to such an extent that the closing component is pushed by the spring component through the retaining ring and, in conjunction with a seat, shuts off the gas flow.
Although with this solution an axial bearing in the open position is achieved, because there is no axial guiding of the ball during the closing stroke there is nothing to prevent the possibility of a sideways deflection of the closing element with the drawback already mentioned in the solution described above.
DE-GM 90 17 534 is another thermal safety device with the same drawback. Here a pre-stressed closing cone with a retaining bolt against a compression spring is aligned in the casing. Whereas the retaining bolt is fixed to the closing cone with its first end, with its second end, the diameter of which is enlarged, it is propped on a pyrometric element, through the central opening of which the retaining bolt juts.
A structurally similar device for shutting off pipes, as described in DE-OS 39 16 100, attempts to counter this drawback by having the retaining bolt held centrally by means of a separate guiding element. The disadvantage with this is that as well as the extra component, high manufacturing costs are involved. In order to assure sufficient guiding the overall dimensions are also increased.
The problem forming the basis of the invention is the development of a thermal safety device of the type mentioned, which has an uninterrupted circular cross section in the area of the closing element. Furthermore, the closing element should be guided axially during the closing stroke. The production costs and the overall dimensions should thus be kept as low and as small respectively as possible.
In accordance with the present invention the problem is solved as follows. In the axial continuation of a seat located within the casing there is a guide pin. On this guide pin a closing spring is aligned, which when taut is located as far as possible inside a blind hole drilled in the closing element. The blind hole has a throat which serves as a control edge. A ram, as part of a detecting element, is on the one side propped on a thermal solder adjacent to the internal wall of the casing, and on the other side on the external surface of the closing element in the area of the control edge, so that the area of the control edge is located off-center. When the safety device is in the open position the ram, under the influence of the closing spring, keeps the control edge adjacent to a click-stop edge.
Once the thermal solder melts away, on the other hand, the control edge is no longer adjacent to the click-stop edge because of the resulting change in position of the ram. Consequently, under the influence of the closing spring, the closing element takes up the closed position. The guide pin then forms a guideway directed towards the seat for the closing spring, and this in turn serves as a guide for movement of the closing element.
A solution has thus been found removing the disadvantage of the background art that the casing has many fittings next to the closing element, particularly in the circulation cross section of the closing element. What particularly makes this solution stand out is its simplicity.
In order to develop the optimum circulation cross section it is especially advantageous if the throat which serves as the control edge is aligned in the blind hole on the end of the closing element facing away from the seat, and furthermore if the external diameter of the closing element in the area of the control edge is substantially smaller than the diameter of the seat.
Other beneficial developments of the invention are indicated in the other patent claims. One particular advantage is if the guide pin is formed by a metal molding, the surfaces of which run parallel to the casing axis lying in the flow direction, and therefore also parallel to the internal wall of the casing. Then only a minimum of flow resistance will be generated by the metal molding. On the end facing away from the closing element the metal molding is connected to the casing, preferably through compression, by means of a widening on both sides, whereby the necessary double-sided widening forms a bearing shoulder for the closing spring at the same time. It is also possible to integrate the click-stop edge into the metal molding.
A particularly good solution is achieved if the click-stop edge is formed by the end of the closing spring facing away from the seat. In addition the guide pin has at least one recess for the end of the closing spring facing away from the seat to click on to.
For reasons of assembly in particular it is also beneficial if the casing has two guide grooves opposite one another to accommodate the widened parts of the metal molding, preferably under the conditions of a force fit.
For reasons of flow as well as assembly it is good if the ram is propped parallel to its longitudinal axis on one side on the widening of the metal molding.